The present invention relates to a drying and/or preheating process for treating coal by entrainment and/or fluidisation in a chamber by means of a heat-transfer gas which is also used to convey the coal pneumatically out of the heat exchange chamber via a duct which brings it to a charging station via a separating device, in which process a hydrocarbon binder in liquid state is injected into the coal during the treatment. The present invention also relates to an installation for carrying out the process.
To improve the quality of coke obtained from dried coal, used in the iron and steel industry, French Pat. No. 1,265,397 proposes adding to the coal, before or after it has been dried, a hydrocarbon binder consisting of a coal tar pitch, an artificial pitch or a bitumen, or also an extract or extraction residue, the hydrocarbon binder being added so that the coal assumes a pasty or liquid consistency. A further known advantage of the introduction of a hydrocarbon binder is that it reduces the amounts of dust clouds when the coal is charged into the coke oven.
Published French Patent Application No. 2,326,464 proposes adding the hydrocarbon binder by spraying and/or by malaxating the coal, the binder being melted or brought into aqueous emulsion beforehand.
French Pat. No. 2,306,252 also proposed introducing the hydrocarbon binder into one of the conveyors of the already preheated coal, and to do this just before the coal is charged, in order to reduce the dust clouds during charging into the coke oven.
However, in the case of a preheating process of the type described above, all these known processes have disadvantages.
In fact, if the binder is introduced into the cold coal, that is to say before the coal is introduced into the dryer and/or preheater, the coal particles which are more or less impregnated with the hydrocarbon binder, are abruptly subjected to the high temperature of the drying and/or preheating fumes, which are sometimes at 600.degree. or 800.degree. C. The effect of this thermal shock is to vaporise some of the hydrocarbon binder, which therefore passes into the vapour phase and is not stopped by the electrofilters, and this reduces the efficiency of the process in preventing the clouds. Moreover, it has been observed that substantial deposits form in the dryer and/or preheater, to the extent of stopping the installation in the case where it is of the internal grinder type.
As regards the process for introducing the hydrocarbon binder into one of the conveyors of the already dried and/or preheated coal, it does not have the advantage of the previous processes, namely the improvement in the collecting efficiency of the separating cyclones.
The object of the invention is to provide a process and an installation which avoid the previous disadvantages, that is to say which simultaneously permit an improvement in the quality of the coke, a reduction in the clouds during charging, and good efficiency of the dust-removing cyclones and hence a reduction in the bulk of the latter.
A further object of the invention is to permit a reduction in the consumption of hydrocarbon binder whenever the quality of the coal to be charged allows. In other words, it must be possible to reduce the consumption of hydrocarbon binder to the amount which is strictly necessary both for good efficiency of the separating cyclones downstream of the dryer and/or preheater operating by entrainment and/or fluidisation, and consecutively for a reduction, or the elimination, of the dust clouds during charging into the oven.